Why should not I update to most recent kernel immediately after release

Question intended for **system administrators.** Consider system running a old but working kernel and all the required functionality is available. (Ubuntu 12.04 LTS specifically with kernel 3.2) Then a new version of kernel is released ( Ubuntu 16.04 LTS with kernel 4.4). Above is just an example case. I have been suggested that I should not immediately update to most recent releases on the production system even if the release has support. Why is it so ? How long should I wait ?